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IOSR Journal of VLSI and Signal Processing (IOSR-JVSP)
Volume 4, Issue 1, Ver. I (Jan. 2014), PP 10-15
e-ISSN: 2319 – 4200, p-ISSN No. : 2319 – 4197
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A Novel CMOS Model Design for 2.4 GHz Narrowband LNA
input matching using inductive Degenerated Topology
M.Ramana Reddy, Dr. N.S Murthy Sharma, Dr. P. Chandra Sekhar
Asst. Professor Dept. of ECE,CBIT Hyderabad
Professor & HeadDept. of ECESVC College of Engg(E.G)
Head & Assoc. ProfessorDept. of ECEOsmania University, Hyd
Abstract: 2.5 GHz narrow band inductive degenerated (LNA) low noise amplifier implemented in a 0.18 µm
RF CMOS process which is used in particularly telecommand system for satellite and also for WSN (Wireless
sensor networks. The amplifier provides a forward gain (S 21) of ˃ 16 db with a noise figure of S 11 ˂ 2db. While
drawing of 10 mw from 1.8v Supply by using inductive coupled degenerated LNA.
General Terms: LNA, Noise figure, gain, linearity.
Keywords:RF CMOS, VLSI Design, Wireless Communications
I.
Introduction
Present days the wireless design suffers from face noise,matching and signal detection.This is a new
challenge for RFIC designers[1][2] .Among the many blocks of the wireless design the crucial block is the low
noise amplifier. The purpose of this block is to match the antenna input with remaining circuitry .To implement
the different topologies of the multi standard transmissions are recognised [9].
Due to low economy higher integration scaling technology the CMOS the competitor for the
implementation of radio transceiver for variouswireless communication system.one of the primary advantage of
using the CMOs is ease of integration with digital section on the single chip. The design of the low noise
amplifier for the satellite is used in wireless telemetry communication system. It is divided into many
subsystems of number of sensors and actuators. One of the subsystems is the master transponder which is facing
earth and then it communicates with the earth station.Remaining subsystems are accessed by this master unit.
By telemetry unit(TMMASTER)the gathered information from the different subsystem are relayed to earth
station(TCMASTER).[9]
Telecommand unit is one which ,the earth station sends the command to control the various
subsystem.However the takes place through respective master unit.dve to the advantage like less weight of
satellites the communication must be through wireless. It is based on IEEE standard.
The first block of receiver is low noise amplifier(LNA).Depending on noise figure and gain the overall
performance of receiver is sustained. The design of low noise amplifier is such that it must present minimum
noise figure and then gain with sufficient linearity.To terminate the unknown length of the transmission line that
deliver the signal from antenna to amplifier.IIP3 provides the 50Ωinput noise amplifier even a good input
match is more sensitive to the quality of the point of terminating impedances .The main reason of the design of
low noise amplifier which is aimed at low power consumption because the standard that is used for
implementation of communication system is at low rate.[9]
1.1 LNA Requirements:
1. Gain (10-20 db) to amplify the received signal and to reduce the input referred noise of the subsequent stages.
2.Good linearity: Handling large undesired signals without much distortion.
3. Low noise for high sensitivity
4. Maximum power gain 50  termination for proper operation and can route the LNA to the antenna which is
located an unknown distance away without worrying about the length of the transmission line [12].
1.2 Basic Topologies
1. Wide band LNA input matching topologies (a) Resistive termination (b) common gate (c) resistive shunt
feedback.
2. Narrow band LNA input matching topologies (a) inductive degenerated (b) resistive terminated [12].
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A Novel CMOS Model Design for 2.4 GHz Narrowband LNA input matching using inductive
1.3 Inductive degenerated LNA:
Fig1: Inductive degenerated low noise amplifier
From Figure1 we can say that Input impedance behaves like a series RLC circuit, due to the addition of Lg in the
circuit[13][5].
g m Ls ..................(1)
1
Zin  s(Lg  Ls ) 
sCga

Cgs
matching occurs when:
Zin  jo   Rs , o2 
L
g L
1
and R s  m s  ωT Ls
Cgs

L
C

g
s
gs
Ls can be selected by: L  Rs if this value is too small to be practical, a capacitor can be inserted in shunt with
s
T
Cgs to artificially reduce ωT][13][5]
Fig2non-idealites of input impedence.
1
1
Zin  s  Lg  Ls  
 ωT L s 
 R Lg  R g  R Ls  R g,NQS
1
sCgs
s
ωT R Ls
(1)
Rs 
Rpoly, sh W
12n 2 L
1
R g,NQS 
5g m
Zin  jω0   T Ls  R Lg  R g  R Ls  R g,NQS (2)
0 
1
(Lg  Ls )(Cgs / /
1
T RL
)
s
inductance loss RLg:offsetZin;RLS: offset Zin and ω0;Gate resistance Rg:offsetZin;NQS gate resistance
Rg;NQS:offsetZin; Q-boosting [5]:
at resonance we get Q boosting effect:
Fig.3. Q-Boosting
Fig.4.equalent circuit for Amplifier input ignoring CgD
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A Novel CMOS Model Design for 2.4 GHz Narrowband LNA input matching using inductive
at resonance we get Q boosting effect:
Q
1
 R s  Ls ωT  Cgs ω0

1
2 Rs Cgs0
(3)
Vgs=Qxvs
Id=gmvs=Qgmvs
Gm
1
2 Rs
 T 
  vs
 0 
Gm
Need to watch out for linearity as vgs is Q times larger than the input signal. Short channel devices operating in
velocity saturation regime (i.e., large overdrive voltage) are more forgiving as their gm is relatively
constant.[13]
Equivalentinput network:
From the source, the amplifier input (ignoring C gd) is equivalent to:
At resonance, the complete circuit is as fig4:
Noise Analysis: from fig5, The output noise current due to Rs and Rg is simply calculated by multiplying the
voltage noise sources by Gm.[13]
The calculation of output noise current due to drain noise is more involved:i 2d flows partly into the source of the
device, it activates the gm. Output Noise current i2d Output noise current: [8]
+
+
(4)
Fig.5. Complete circuit at Resonance
Fig.6. Q-Boosting Noise Analysis
Fig.7. Q-Boosting Noise Analysis-Drain Noise
Gm 
1
2 Rs
 T 
 
 o 
Drain Noise: The noise component flowing into the source is given by the current divider:
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A Novel CMOS Model Design for 2.4 GHz Narrowband LNA input matching using inductive
 gs  
j Ls 
( g m gs  id ) X j Ls
  g m j Ls
1
1
 j Lg  Rs X
jCgs
jCgs
(5)
  g m gs  id  X
g ms  
id
2
jLs
1
 at resonance  X
jCgs
Rs
(6)
here we are not including Rg in the small signal model.
Total Output Noise: Let's first ignore the correlation of the gate noise and drain current noise. Notice only one
forth of the drain noise flows to output.


1
ino2  Gm2 VRs2  VRg2  id2 (7)
4
Gm 
F
ino2
2
m
2
1  T 


2 Rs  o 
=1+
G VRs
Rg
Rs

 

g R  o
 m s  T 
(8)
2
Note that the Noise figure at resonance is the same as CS amplifier w/o inductive degeneration. Inductive
degeneration did not raise Fmin but matched the input.If we consider the correlation of the gate noise and drain
current noise then one can show.
F  1+
Rg
Rs

  1  2 c QL
QL  QCgs 
 

 g m Rs  o 

 T 
2
(9)
 2  2
(10)

(1  QL2 )
5
5
0 (L g  L s ) (11)
1

0 RsCgs
Rs
Optimal Noise figure happens for a particular QL. Possible to obtain a noise and power match.[14]
OptimalQL : If we try to optimize the noise figure while power dissipation is kept constant then:
i.QL,opt will be independent from the frequency and around 4.5
ii. Fmin is not too sensitive to QL and only changes by less than 0.1dB for QL between 3.5 and 5.5
iii. Smaller QL results in larger bandwidth and smaller inductors, while a larger Q L results in narrower
bandwidth and larger inductors.
Linearity: Linearity of a MOS transistor in saturation region:[13][14][5]
4 Veff
 2  Veff
3 
1  V   83
Veff  Vgs  Vth
1
VIIP 3 ,strongMOS 
eff

Veff

Esat L
Esat 1V /  m
for L 0.35 m  0.18 m
IIP3 is independent of W
V 2 IIP 3 , LNA V 2  
2
 1
16 PD
 2    1  
3 Po2 2
 
  Veff
Po 
3
(13)
3 Vsat Esat
VDD
2 o Rs
Effect of RL on input match: We ignored the effect of load impedance on input impedance in previous
derivations. It can be shown that[13]
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A Novel CMOS Model Design for 2.4 GHz Narrowband LNA input matching using inductive
2
ZIN 
( L  ) (14)
ro
1
 jLS  
[ LS S  S ]
jCGS 
ro  RL  jLS 
ro

r
1
 jLS   o [ Ls wr ]
jCGS
ro  RL
RL can be large and it can drop the real part of the input impedance when we use resonators at output. Notice
that the output impedance influenced the input impedance even in the absence of C gd
Design Recipe for Inductive degenerated of LNA:
Step1: Choose QL for optimal[13]
NF CgsWidth(W)


1
 QL 

O RS CGS 

Step2: Determine the current Id from power budget.
Step3: From W & IdWidth(W)
Step4: From gm and VeffT andFmin
Step5: Select Ls and Lg for the input network
Ls 
Rs
T
 1
Lg   2
 C
 0 gs

  Ls

Design Recipe Iterations: If NF is not low enough, increase T by increasing Id(with fixed device size) and for
a fixed current density, increasing Q will reduce device size thus reduce total power and hence NF will increase.
If the Linearity does not meet, reduce Q, burn more current and apply proper linearization techniques. If we
need to increase gain, choose larger QL,Larger gm and larger Load (ZL) [13][2].
II. Simulation Result Analysis
M1
M2
Lg
Ls
Id
ZL
Calculated
110 m/0.18
110 m/0.18
31nH
0.14nH
9mA
2.4 
Simulated
110 m/0.18
110 m/0.18
20nH
0.28nH
8.6mA
26 
TABLE-1. PARAMETERS
Frequency
S11
S21
NF
IIP3
Current
Supply
Specs
2.4Ghz
-10dB
16 dB
2dB
10dBm
10mA
1.8V
Simulation
2.4Ghz
- 32 dB
15.7dB
 0.62dB
-6.85dBm
8.6mA
1.8V
TABLE-2. PERFORMANCE
The design was simulated using the ADS and also cadence tools provided for the 18mRF CMOS process. The
following graphs shows S21,S11, noise figure, IIP3, stability factor of inductive degenerated LNA
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A Novel CMOS Model Design for 2.4 GHz Narrowband LNA input matching using inductive
Fig 8(a)S11 parameters(b)noise figure and (c)S21 parameters.
III.
Conclusion
The design of receiver supporting 4G wireless applications in all bands presents many challenges.
Some of the characteristics of the receivers are multi band multi standard operation, MIMO support, low power
and low cost. By applying mathematical descriptions for key performance parameters of LNA is required 4G
front ends. This paper has presented the design of gain S21 16dB with a noise figure 2dB while drawing 10mW
power from 1.8 volts supply by using inductive coupled degenerated LNA topology. A lesson learned in this
design is the importance of intuitive understanding of resonance and circuit theory when designing LNAs using
wireless telemetry telecommand system and also for wireless sensor network.
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